1. Field of the Invention
The present invention relates to a shrinkage band for a CRT, and more particularly, to a shrinkage band combined to a CRT adopting a panel with a flat outer surface and a curved inner surface recently emerging as a new trend, which is capable of preventing occurrence of a explosion phenomenon on the panel.
2. Description of the Background Art
As is widely known, a CRT is a display instrument used for an observation of an oscilloscope or a radar as well as a television set.
The CRT serves to transmit a color image for users"" viewing which is reproduced in a manner that a phosphor screen consisting of fluorescein pixels, that is, an electrooptic device, converting a video data received as an electric signal to a visual information, graphite, that is, an optical absorption substance, and an aluminum film improving a luminance, is hit by an electronic beam.
FIG. 1 illustrates a construction of a general CRT in accordance with a conventional art.
As shown in the drawing, the conventional CRT includes a panel 1 positioned in the front surface and a funnel 2 adhesively attached to the rear end of the panel 1, forming a vacuum outer casing container.
An electric gun 5 radiating an electric beam 4 is hermetically sealed inside a neck portion 3, that is, the end portion having relatively smaller diameter in the funnel 2. A deflection yoke 9 for generating a pin-cushion-type horizontal deflection magnetic field and barrel-type vertical deflection magnetic field, is mounted in the outer circumferential side in the vicinity of the neck portion 3, so as to deflect the radiated electronic beam to the whole screen.
A phosphor film 6 is formed on the inner surface of the panel 1, and a shadow mask 7 having a section-based electrode function is supported by a frame 8 installed therein, spaced apart at a predetermined distance from the phosphor film 6.
In the conventional CRT constructed as described above, the electronic beam 4 radiated from the electronic gun 5 is deflected to a desired portion of a screen by the vertical and horizontal deflection magnetic fields of the deflection yoke 9, and as the electronic beam passes through a plurality of through holes (not shown) formed at the shadow mask 7, it hits the phosphor film 6, thereby creating a picture.
Since the inside of the conventional CRT constructed as above makes a vacuum state by the panel 1 and the funnel 2, a stress is applied to the panel due to an external atmosphere pressure. That is, as shown in FIG. 2, according to the structural characteristics of the CRT, the front surface portion of the panel 1 receives a compressive stress while the side portion thereof receives a tension stress.
Thus, in a state that the compressive stress and the tension stress work due to the vacuum, when an external impact is applied to the CRT, a explosion phenomenon possibly causing that the panel 1 or the funnel 2 is exploded may occur, which, thus, causes a malfunction to the CRT as well as threatening users"" safety.
In order to prevent such a explosion phenomenon, a shrinkage band 10 is typically combined to continuously cover the external side portion of the panel 1.
The panel 1 is formed of a glass, which is weaker over the tension stress compared to the compressive stress in its property, and accordingly, the side portion of the panel 1 is structurally weaker compared to the front surface portion thereof.
Therefore, the shrinkage band 10 is combined to the CRT so as to strengthen the rigidity of the side portion of the panel 1 where the tension stress is concentrated, to thereby prevent the explosion phenomenon.
In detail, when an impact is applied to the surface of the CRT, a deformation stress, that is, a tension stress, expanding the side portion of the CRT is generated, which is, however, restrained by the rigidity of the shrinkage band 10 that compresses the side portion, so that a crack possibly caused passing the side portion and the surface portion can be restrained or the speed of the crack can be lowered down. And, at the same time, the direction of the main stress to the surface portion of the panel 1 and the proceeding direction of the crack are changed, thereby preventing the explosion phenomenon.
According to a research, the maximum tension stress working on the side portion of the panel 1 was observed by 87.9 kgf/cm2 without the shrinkage band 10, while when the shrinkage band is combined to the side portion of the panel 1, the maximum tension stress was observed by 79.0 kgf/cm2.
The panel 1 is typically fabricated by molding. When the panel is fabricated by molding, a mold match line is formed in the panel 1, and the shrinkage band 10 is generally combined to the CRT in a manner that it covers the mold match line 11, as shown in FIGS. 3A-3B.
Referring to kinds of the shrinkage bands, there are a straight line-type shrinkage band 10xe2x80x2 which is directed to highly improve an adherence of the shrinkage band itself for heightening the compression efficiency as shown in FIG. 3A and a fold-type shrinkage band 10xe2x80x3 directed to strengthening a compression force in the front portion of the panel 1 as shown in FIG. 3B.
Theoretically, though it is desired to install the shrinkage band 10xe2x80x3 on the basis of the center of the curved portion of the corner portion, making a break-even point of the compression efficiency, of the inner surface of the panel 1, since the mold match line 11 and the position of the center of the curved portion of the corner are almost the same owing to the spherical panel form, substantially the mold match line 11 is easily identified in view of form is used as an installment reference to the shrinkage band 10.
In detail, since, on the basis of the mold match line 11, the upper portion of the shrinkage band 10 compresses the front portion of the panel 1 and the lower portion of the shrinkage band 10 compresses a skirt portion of the panel 1, the shrinkage band 10 is to be positioned suitably on the basis of the mold match line 11 in order to improve a explosion prevention capacity.
For example, if the shrinkage band 10 is inclined toward the lower portion (the skirt portion of the panel 1) of the mold match line 11, many cracks can be made in the CRT due to an external impact, or in a worse case, the panel 1 may be separated from the CRT.
Reversely, if the shrinkage band 10 is inclined toward the upper portion (the front portion of the panel 1) of the mold match line 11, a explosion or a crack can be easily made in the skirt portion of the panel 1 due to an external impact.
Actually, when the shrinkage band 10 is combined to the CRT, in order to accomplish optimum explosion-proof characteristics, the mold match line 11 is typically designed in a manner that the compression force of the upper portion is weak compared to that of the lower portion. Taking an example that the spherical panel as in the conventional art is adopted to the CRT, it is designed in a manner that the compression force of the upper portion of the mold match line 11 does not go beyond 90% compared to the compression force of the lower portion.
As another way of preventing the explosion, besides the shrinkage band 10, a strong glass having an improved explosion prevention characteristics by heightening its rigidity may be used for the panel 1, or a film may be attached onto the surface of the panel 1 so as to provide a explosion prevention function.
Meanwhile, recently, as a screen is turning large-sized and flat in order to provide a distinct image, there has been proposed a panel (termed as a xe2x80x98flat panelxe2x80x99, hereinafter) of which an outer surface is flat while inner surface is curved. This kind of panel offers a distinct image compared to the general spherical panel as used in conventional arts, implementing a highly-refined picture, but the corner portion of the panel is formed thick compared to that of the general spherical panel.
That is, the thickness ratio between the center and the corner of the general spherical panel is approximately 1.3, while in case of the flat panel, the thickness ratio between the center and the corner is approximately 1.8xcx9c2.0.
Accordingly, in case that the reference for distribution of the compression force of the shrinkage band of the flat panel is applied by the mold match line in the same manner as in the case of general spherical panel, the position of the shrinkage band becomes relatively inclined backwardly of the panel, causing a weakness in the front side of the panel, which creates a problem in that there is a high possibility that a crack or a explosion is made in the front side of the panel.
Meanwhile, in order to prevent such a explosion phenomenon, the strong glass may be employed to the panel or the film may be attached onto the surface of the panel. However, in the former case, a production cost is inevitably increased in spite of the explosion prevention effect, while in the latter case, its expense is increased and recycling is impossible.
Therefore, an object of the present invention is to provide a shrinkage band for a CRT combined to a flat panel in a suitable position which is determined from the forward or backward direction of the panel on the basis of a line extended in the horizontal direction from the center of the curved portion of the corner of the inner side of the flat panel, so as to prevent a explosion phenomenon on the flat panel.
To achieve these and other advantages and in accordance with the purposed of the present invention, as embodied and broadly described herein, there is provided a shrinkage band for a CRT including: a panel forming a display screen; and a shrinkage band having a predetermined width combined to cover the outer circumferential surface of the side portion of the panel in a state of satisfying an inequality 0.95xe2x89xa6Fa/Fbxe2x89xa61.39 on the assumption that an engagement tensile force of the front side of the panel is Fa and that of the opposite side of the front side of the panel is Fb, on the basis of the line extended in the horizontal direction of the panel from the center of the curved portion of the corner of the inner side of the flat panel.